FIG. 12 illustrates a typical small camera module 100 used on a cellular phone equipped with a camera and other similar electronic devices comprises a lens module 101 containing lenses, an intermediate part 102 provided on the outside of the lens module 101, and a base 103 on which the intermediate part 102 equipped with the lens module 101 is mounted.
The lens module 101 is formed in a cylindrical shape, and contains a lens L1 and a lens L2 inside. A screw thread 104 is formed on the cylindrical surface of the lens module 101.
The intermediate part 102 is a ring-like part and a screw thread 105 that fit with the lens module 101 is provided on its internal cylindrical surface. The engagement between this screw thread 105 and the screw thread 104 of the lens module 101 accomplishes the assembling of the lens module 101 into the intermediate part 102. Furthermore, a screw thread 106 is provided on the outer cylindrical surface of the intermediate part 102 as well.
The base 103 provides a cylindrical space, in which a screw thread 107 is provided to engage with a crew thread 106 of the intermediate part 102, and a light receiving unit 108 is affixed to the bottom of the cylindrical space. The intermediate part 102 carrying the lens module 101 is mounted on the base 103 as the screw 106 of the intermediate part 102 is engaged with the screw thread 107 of the base 103.
The camera module 100 is normally shipped out from the factory after adjusting the focus so that an image of the lens module 101 can be focused properly on the light receiving unit 108 by means of the screw threads 106 and 107 of the intermediate part 102 and the base unit 103 respectively.
In order to use the camera module 100 utilizing its macro function, it is necessary to adjust the engagement condition of the screw threads 104 and 105 that unite the intermediate part 102 and the lens module 101 while using the equipment the camera module 100 is attached to.
To activate the macro function of the camera module 100, it is necessary to change its focal distance by moving the lens module 101 inside the intermediate part 102. However, this causes the pitch of the screw threads 104 and 105 that unite the lens module 101 and the intermediate part 102 to be too fine as overall compacting of the camera module 100 is demanded, which forces the lens module 101 and the intermediate part 102 to be smaller, thus preventing the screw threads 104 and 105 from having a coarser pitch.
Consequently, a large rotary angle of the lens module 101 is required in order to relocate it relative to the intermediate part 102 for changing from the normal use condition to the macro use condition. This causes a problem in that it is difficult to provide the macro function of the micro camera module 100 when used on devices such as cellular phones. More specifically, the problem is that it is, practically speaking, impossible to switch from the normal to macro condition on a compact camera module 100 with as screw pitch of 0.3 mm or so as it requires a rotary angle of half a revolution (180°) to one revolution (360°) in order to achieve a switching distance of 0.15 mm to 0.3 mm. Any attempt to use a larger screw thread form to minimize the required rotary angle would end up in a problem that a larger pitch screw thread means a larger thread height, thus defeating the intention of minimizing the overall size of the camera module.